Metastasis, the process by which tumor cells disseminate throughout the body and colonize distant sites, continues to be a principal cause of cancer-associated death. Despite intense research, the cell biological mechanisms regulating metastasis remain incompletely understood. The objective of this proposal is to test the hypothesis that autophagy, a cellular self-digestion process, is a critical determinant of metastasis. This goal is motivated by in vitro data demonstrating that autophagy regulates two essential cell phenotypes for metastasis: (1) adhesion independent survival and (2) cell invasion and migration. During metastasis, tumor cells must survive in the absence of stable cell-extracellular matrix contacts in order to undergo adhesion changes necessary for motility during invasion, to survive in the absence of adhesive contacts while traversing the circulation to the target site, and to survive in the unaccommodating, hostile foreign microenvironment of the target site. Cell invasion is essential for both the earliest and later stages of metastasis, in whch cells from the primary tumor mobilize towards blood vessels and tumor cells in the circulation exit the vasculature to seed the foreign site, respectively. The following proposed specific aims will extend these in vitro results and validate if and how autophagy regulates metastasis in vivo: (1) Determine the functional contributions of autophagy to metastasis in vivo. The effects of genetic autophagy inhibition on breast cancer metastasis to lung in the polyoma middle T mouse model of metastasis (MMTV-PyMT) will be determined. (2) Determine the effects of autophagy on cell polarity during migration. The effects of autophagy on inhibition of front-rear cell polarity, which is necessary for directed, chemotactic invasion in vivo, will be established i vitro using time-lapse imaging technologies. These studies will broaden our understanding of the mechanisms underlying metastasis, and in doing so, potentially expose autophagy as a innovative route for therapeutic intervention against metastatic disease.